The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to methods of improving hot carrier parameters in a field-effect transistor by hydrogen reduction.
Complementary-metal-oxide-semiconductor (CMOS) processes may be used to build a combination of p-type field-effect transistors (pFETs) and n-type field-effect transistors (nFETs) that are coupled to implement logic gates and other types of integrated circuits, such as switches. Field-effect transistors may include a source, a drain, a channel region between the source and the drain, a gate electrode, and a gate oxide arranged between the gate electrode and the channel region. When a control voltage exceeding a designated threshold voltage is applied to the gate electrode, a device output current is produced by carrier flow in the channel region between the source and drain.
Arsenic may be implanted as an n-type dopant to form source and drain extensions. As shown in FIG. 1A, the junctions with the channel region on both the source side and the drain side are abrupt in this circumstance. Alternatively, arsenic and phosphorus may be co-implanted as n-type dopants to form source and drain extensions. As shown in FIG. 1B, the junctions with the channel region are broadened on both the source side and the drain side due to the inward diffusion of phosphorus.
Device reliability is an ongoing issue for semiconductor manufacturing and development. One of the detractors for reliability is attributed to hot carrier effects. In particular, the effects of hot carrier stress may degrade the performance of a field-effect transistor over time by damaging the drain side of the channel and the gate oxide. During hot carrier stress testing of a field-effect transistor to simulate actual device operation, a constant voltage is applied to the drain and the gate. As shown in FIG. 1C, hot carriers moving from the source to the drain may cause hydrogen release from the gate oxide at the drain side of the channel by breaking hydrogen-oxygen bonds. The released hydrogen may prompt the passivation or deactivation of phosphorus on the drain side of the channel by, for example, attracting electrons from the dopant or by forming bonds with the dopant. Because of the hydrogen passivation, hot electron stress causes the junction at the drain side to become abrupt, whereas the junction on the source side remains broad. Due at least in part to development of this asymmetry, the device drive current may degrade over time.
Improved methods of improving hot carrier parameters in a field-effect transistor by hydrogen reduction are needed.